1. Field of the Invention
The invention relates to a sealing system for restricting leakage of fluid around a piston rod interconnecting a piston located in a cyclical high pressure piston cylinder and a crosshead located in a lower pressure, crankshaft space. More particularly, the invention relates to an improved sealing system having a seal element around the piston rod within an intermediate chamber between the crankshaft space and the piston cylinder where the improvement is a means for reducing the radial forces on the seal element caused by the piston rod.
2. Description of the Prior Art
In a hot gas engine, such as one using the Stirling cycle, many solutions have been developed to prevent leakage of the working gas from the piston cylinder into the crankshaft space and leakage of lubrication fluid in the crankshaft space into the piston cylinder. Most of this leakage occurs around the piston rod which interconnects the piston in the piston cylinder with the crankshaft in the crankshaft space.
One type of sealing system is disclosed in U.S. Pat. No. 3,848,877 to Bengtsson et al, of common assignment with present invention. The system taught in Bengtsson et al is effective in preventing fluid flow between the piston cylinder and crankshaft space by providing around the piston rod between the piston cylinder and crankshaft space a seal element in the form of a ring having a conical cross section which is urged against the piston rod by mating spring-loaded metal wedge rings. However, because of the differences in radial play of the piston in the cylinder and of the crankshaft crosshead in the crankshaft space, the piston rod imposed radial stresses on the seal element thereby reducing the effectiveness and durability of the seal element.
The piston in its piston cylinder has very little space in a radial direction in which to move, however, the crosshead in the crankshaft space which interconnects the piston rod with the crankshaft has significantly greater radial space for movement. This greater radial movement of the crosshead causes the piston rod to exert substantial radial forces on the seal element usually located in an intermediate chamber between the piston cylinder and the crankshaft space. Because the radial forces vary in a cyclical manner, they are detrimental to the function of the sealing system surrounding the piston rod. Breakdown of the seal element in the sealing system or its distortion due to the radial forces of the piston rod reduces the sealing system's effectiveness in restricting fluid flow between the crankshaft space and the intermediate chamber. Such reduced effectiveness may permit the escape of working gas from the piston cylinder through the intermediate chamber into the crankshaft space or permit the leakage of lubricating oil from the crankshaft space into the intermediate chamber.
The present invention is intended to provide a remedy to the problems engendered by the radial movement of the piston rod. The invention allows relative radial movement between the piston rod and the crosshead, thus minimizing the radial forces of the piston rod on the seal element. Furthermore, the invention provides a means for more effectively securing the seal element in the intermediate chamber in opposition to the minimized radial forces of the piston rod.
The advantages offered by the invention permit the necessary radial play of the crosshead, which may be significantly greater than the radial play of the piston in the piston cylinder, while substantially reducing the radial play of the piston rod at the seal between the intermediate chamber and the crankshaft space. This reduction in radial movement of the piston rod increases the effectiveness of, and prolongs the life of, the sealing system.